docker-qemu/start-qemu

#!/bin/bash
set -e

# main available options:
#   QEMU_CPU=n    (cores)
#   QEMU_RAM=nnn  (megabytes)
#   QEMU_HDA      (filename)
#   QEMU_HDA_SIZE (bytes, suffixes like "G" allowed)
#   QEMU_CDROM    (filename)
#   QEMU_BOOT     (-boot)
#   QEMU_PORTS="xxx[ xxx ...]" (space separated port numbers)
#   QEMU_NET_USER_EXTRA="net=192.168.76.0/24,dhcpstart=192.168.76.9" (extra raw args for "-net user,...")

hostArch="$(uname -m)"
qemuArch="${QEMU_ARCH:-$hostArch}"
qemu="${QEMU_BIN:-qemu-system-$qemuArch}"
qemuArgs=()
qemuPorts=( 22 $QEMU_PORTS )

if [ -e /dev/kvm ]; then
	qemuArgs+=( -enable-kvm )
elif [ "$hostArch" = "$qemuArch" ]; then
	echo >&2
	echo >&2 'warning: /dev/kvm not found'
	echo >&2 '  PERFORMANCE WILL SUFFER'
	echo >&2 '  (hint: docker run --device /dev/kvm ...)'
	echo >&2
	sleep 3
fi

qemuArgs+=( -smp "${QEMU_CPU:-1}" )
qemuArgs+=( -m "${QEMU_RAM:-512}" )

if [ "$QEMU_HDA" ]; then
	if [ ! -f "$QEMU_HDA" -o ! -s "$QEMU_HDA" ]; then
		(
			set -x
			qemu-img create -f qcow2 -o preallocation=off "$QEMU_HDA" "${QEMU_HDA_SIZE:-8G}"
		)
	fi
	# http://wiki.qemu.org/download/qemu-doc.html#Invocation
	#qemuArgs+=( -hda "$QEMU_HDA" )
	qemuArgs+=( -drive file="$QEMU_HDA",index=0,media=disk,discard=unmap )
fi

if [ "$QEMU_CDROM" ]; then
	qemuArgs+=( -cdrom "$QEMU_CDROM" )
fi

if [ "$QEMU_BOOT" ]; then
	qemuArgs+=( -boot "$QEMU_BOOT" )
fi

netArg='user'
netArg+=",hostname=$(hostname)"
if [ "$QEMU_NET_USER_EXTRA" ]; then
	netArg+=",$QEMU_NET_USER_EXTRA"
fi
for port in "${qemuPorts[@]}"; do
	netArg+=",hostfwd=tcp::$port-:$port"
	netArg+=",hostfwd=udp::$port-:$port"
done

qemuArgs+=(
	-net nic
	-net "$netArg"
	-vnc ':0'
	-serial stdio
	"$@"
)

set -x
exec "$qemu" "${qemuArgs[@]}"